reporter: now the defensive marriage act known as doma first passed by congress and signed by president clinton in 1996 is being challenged at the supreme court. >> being asked to decide there. whether or not congress can pass a law that treats same-sex couples who are already married under the laws of their state different from opposite sex couples. >> reporter: defenders of the law say congress has as much right as the states to make its own definition of marriage. >> doma is important because congress said it was important. we sent our elected representatives to washington, d.c., and they chose to say that marriage is one man and one woman for federal law. >> reporter: conservatives say the founding fathers never contemplated gay marriage. >> it's clearly not what anyone understood as marriage at the time of the framing of the constitution. >> reporter: still, same-sex family as pay taxes and don't get the same benefits. the issue with doma gets complicated if they have children who are also excluded from benefits. >> when we have kid, i would like them to be born in a post-doma united state